Cervical vertebra plate

ABSTRACT

The invention relates to a cervical vertebra plate ( 10 ) for osteosynthesis, having two receiving openings for the screw heads ( 18 ) of bone screws ( 16 ) in order to secure the cervical vertebra plate to two cervical vertebrae. The receiving openings have grooves ( 22 ) in the distal region on the periphery thereof and the depth of the grooves increases from a proximal to a distal end. The invention also relates to a bone screw ( 18 ) comprising a screw head ( 16 ) and a screw shank. The screw head comprises grooves ( 34 ) on the outer periphery thereof and the depth of the grooves varies along the length thereof.

This application is the national stage of PCT/EP2003/010104 filed onSep. 11, 2003 and also claims Paris Convention priority of DE 102 43791.2 filed on Sep. 17, 2002.

BACKGROUND OF THE INVENTION

The invention concerns a cervical vertebra plate for osteosynthesis,having at least two receiving openings for the screw heads of bonescrews to secure the cervical vertebra plate to two cervical vertebrae,wherein the receiving openings have a fluting, in particular alongitudinal fluting, in the distal region about the periphery thereof.The invention also concerns a bone screw, in particular, for a cervicalvertebra plate of this type, comprising a screw head and a threadedscrew shank, wherein the outer periphery of the screw head has afluting, in particular, a longitudinal fluting.

Bone plates are known per se, e.g. from DE 199 50 270 A1. Bone plates ofthis type are e.g. secured to vertebrae to orient and stabilize them.Towards this end, the individual bone plates are connected via rods,wherein the rods are mounted, in particular clamped, to the bone plates.

Bone screws are used to secure the bone plates to vertebrae. The screwspenetrate through the bone plates and are screwed into the vertebra. Thebone plate is usually held via the screw head.

U.S. Pat. No. 5,275,601 also discloses a bone screw which is supportedwith its fluted conical screw head in a receiving opening of a plate.The plate is secured to the bone via these screws.

It is the underlying purpose of both of these bone plates to optimallyadopt the forces acting on the bone such that they are eithertransferred to a neighboring bone or bone part or to correction orfixation rods. Towards this end, the screw head must in any case beoptimally supported in the receiving opening of the bone plate toprevent play between the screw head and receiving opening. Securing toprevent inadvertent unscrewing is effected by the fluting provided onthe inner periphery of the receiving opening and/or the outer peripheryof the screw head.

It is the underlying purpose of the present invention to introduce asystem which provides a safer, tight connection, i.e. optimum support ofthe outer peripheral surface of the screw head on the inner peripheralsurface of the receiving opening of the bone plate.

This object is achieved in accordance with the invention with a cervicalvertebra plate of the above-mentioned type in that the depth of thefluting increases from a proximal to a distal end.

SUMMARY OF THE INVENTION

The inventive cervical vertebra plate also has a fluting on the innerperiphery of the receiving opening. However, the depth of the fluting isnot constant but increases in the distal direction. The fluting mayextend over the entire length of the receiving opening. This is,however, not absolutely necessary. In the inventive cervical vertebraplate, the screw head is advantageously positively supported on theproximal side of the receiving opening over a large area of the innerperipheral surface. This region of positive support gradually decreasesin a distal direction. The tight support of the screw head in theproximal area ensures that the bone plate is optimally and positivelyheld in the direct vicinity of the bone by the bone screw. The forcesexerted on the bone are thereby introduced into the bone plate directlyat the bone surface via the bone screw, i.e. via the screw head. This isadvantageous in that no bending moments act on the screw and the screwmay therefore be smaller in size as is particularly important in theregion of cervical vertebrae, since these vertebrae are small andprevent use of large implants.

To improve the seat of the bone screw, in particular its positivelocking, the receiving openings in the cervical vertebra plate widen ina distal direction. The receiving openings are advantageously conical ordome-shaped. The screw head may thereby be sunk in the cervical vertebraplate to positively abut the inner peripheral surface of the receivingopening when the screw is tightened.

The fluting is preferably wedge-shaped. The conical flanks which facethe inner space of the receiving opening, can thereby advantageously diginto the outer surface of the screw head or hook to the screw head, toprovide protection against unscrewing.

In a preferred embodiment, the cervical vertebra plate has fourreceiving openings which are located in the corner regions of thecervical vertebra plate. In this manner, two neighboring cervicalvertebrae can be secured to the cervical vertebra plate using two bonescrews each. This permits transfer of tensile and compression forces andalso of torsion and shearing forces.

In a further development, a further receiving opening is provided in thecenter of the cervical vertebra plate. A bone screw may be screwed intothis further central receiving opening, in particular if the vertebraeare incomplete or difficult to access, to provide a further possibilityof connecting this vertebra to the cervical vertebra plate.

The above-mentioned object is also achieved in accordance with theinvention with a bone screw of the above-mentioned type in that thefluting has a varying depth along its length.

In this manner, the supporting region on the outer peripheral surface ofthe screw head, with which the screw head positively abuts the innerperipheral surface of the receiving opening is enlarged as is the casefor the inner peripheral surface of the receiving opening of thecervical vertebra plate. Optimum, secure force transfer between thevertebra and the cervical vertebra plate is thereby also facilitated bythe bone screw.

In a further development, the screw head is substantially a truncatedcone and the depth of the fluting increases from the proximal to thedistal end. This is advantageous in that the supporting area, i.e. Thearea of the screw head which positively abuts the inner peripheralsurface of the receiving opening is located in the proximal area. Inthis fashion, the forces are introduced from the vertebra into thecervical vertebra plate directly at the vertebra surface, as wasmentioned above. The vertebra is supported without substantial bendingforces acting on the bone screw, which allows the bone screw to berelatively small in size.

In another embodiment, the screw head is substantially spherical and thedepth of the fluting increases from the poles in the direction of theequator, in each case. The individual sections of the flutingsubstantially have the shape of a spherical segment such that the screwhead has large supporting surfaces in the distal area and also in theproximal area.

The longitudinal fluting is preferably formed by wedge-shaped,substantially longitudinal grooves with the individual grooves beingseparated from each other. As viewed in the peripheral direction, thereare smooth sections between the fluting. These areas without groovesalso provide positive abutment of the screw head on the inner peripheralsurface of the receiving opening of the cervical vertebra plate, tofacilitate screwing of the screw. Screwing of the screw is not impairedby the fluting on the inner peripheral surface of the receiving openingor on the outer peripheral surface of the screw head, and the supportingarea is also enlarged.

The length of the area without grooves, viewed in the peripheraldirection, preferably corresponds to 0.3 and 2.0, in particular between0.5 and 1.0 times the length of the grooves themselves. In case ofsmaller or narrower areas without grooves, the screw head may bend moreeasily during screwing or directly before screwing is terminated to hookwith the grooves or with the fluting in the receiving opening of thecervical vertebra plate and thereby be secured against unscrewing. Ifthere are large regions without grooves, the screw head has relativelylarge abutment surfaces to assure optimum force transmission.

Further advantages, features and details of the invention can beextracted from the following detailed description of preferredembodiments with reference to the drawings. The features shown in thedrawing, and mentioned in the description and the claims may beessential to the invention either individually or in arbitrarycombination.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a perspective view of a cervical vertebra plate withinserted bone screws;

FIG. 2 shows an enlarged illustration of a corner area of the cervicalvertebra plate showing a receiving opening; and

FIG. 3 shows a perspective view of a bone screw.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a cervical vertebra plate which is designated in total by10 and has a substantially H-shape. The corner regions 12 have receivingopenings 14 (FIG. 2) which receive screw heads 16 (see also FIGS. 3 and4) of bone screws 18. The cervical vertebra plate 10 has a furtherreceiving opening in its center which bears a further bone screw 18.

The cervical vertebra plate 10 connects two cervical vertebrae, whereintwo bone screws 18 are screwed into one cervical vertebra and the twoother bone screws 18 are screwed into the other cervical vertebra. Thecentral bone screw is used if a cervical vertebra is incomplete or ifone of the bone screws 18 disposed in the corner areas 12 cannot bescrewed into a cervical vertebra.

The receiving opening 14 has an inner peripheral surface 20 which isprovided with fluting 22, in particular, a longitudinal fluting (FIG.2). The fluting 22 extends from the distal end 24 of the receivingopening 20 but not entirely to the proximal end 26, rather merelythrough approximately 80% of the thickness of the cervical vertebraplate 10. The depth of the fluting 22 changes along the height of thereceiving opening 14 and increases from the proximal end 26 towards thedistal end 24, thereby producing a fluting 22 with approximatelywedge-shaped grooves 28. Neighboring grooves 28 border areas 30 withoutgrooves. These areas 30 without grooves provide positive abutment of thescrew head 16 and force transfer between screw head 16 and cervicalvertebra plate 10.

FIG. 2 also shows that the width of the areas 30 without groovesincreases in the proximal direction such that the screw head 16positively abuts over the entire periphery in the region of the proximalend 26.

Fig 3 shows an embodiment of a bone screw 18 having a spherical screwhead 16. The outer periphery 32 of the screw head 16 is also providedwith a fluting 34 which is formed by the spherical segment-shapedgrooves 36. The depth of each groove 36 thereby increases from theproximal end of the screw head 16 towards the distal end and decreasesagain from the equator (maximum diameter of the screw head 16). An area38 without grooves is also provided between the individual grooves 36,whose width increases from the equator in the direction towards theproximal and distal ends.

The fluting 22 of the cervical vertebra plate 10 and the fluting 34 ofthe bone screw 18 are designed to permit screwing in of the bone screw18 but exert a blocking effect in the opposite direction such that thebone screw 18 does not loosen in the receiving opening 14 due to slightunscrewing.

1. A system for osteosynthesis, the system comprising: a cervicalvertebra plate having at least two receiving openings for screw heads ofbone screws to secure said cervical vertebra plate to two cervicalvertebrae, wherein said receiving openings have a first fluting,disposed about a periphery of a distal area, wherein a depth of saidfirst fluting increases from a proximal towards a distal side of saidopenings; and a bone screw having a screw head and a threaded screwshank, wherein a outer periphery of said screw head has a second flutinghaving a varying depth along a length thereof, wherein said screw headis substantially spherical and said second fluting has a depth whichincreases from each pole towards an equator of said screw head.
 2. Thesystem of claim 1, wherein said first and said second fluting extend ina longitudinal direction.
 3. The system of claim 1, wherein saidreceiving openings widen in a distal direction.
 4. The system of claim3, wherein said openings widen in a conical or dome-shaped fashion. 5.The system of claim 1, wherein said first and said second flutings arewedge-shaped.
 6. The system of claim 1, wherein said plate has fourreceiving openings which are located in corner areas of said plate. 7.The system of claim 6, wherein said plate has a further receivingopening disposed in a center of said plate.
 8. The system of claim 1,wherein said first fluting is formed by wedge-shaped grooves whichextend in a substantially longitudinal direction, individual grooveshaving a mutual separation bordering groove-free regions.
 9. The systemof claim 1, wherein said second fluting is formed by wedge-shapedgrooves which extend substantially in a longitudinal direction, withindividual grooves being separated from each other.
 10. The system ofclaim 1, wherein, viewed in a peripheral direction, areas withoutgrooves are disposed between groves of said first and said secondfluting.
 11. The system of claim 1, wherein, viewed in a peripheraldirection, a length of said area without grooves is between 0.3 and 2.0or between 0.5 to 1.0 times a length of said groove.
 12. The system ofclaim 1, wherein said first and said second fluting are structured anddimensioned to cooperate with another to allow said bone screw to bescrewed into the cervical vertebra and, following completion of ascrewing procedure, to block rotation which would loosen said bonescrew.